Acknowledgements
We thank the patients for their valuable collaboration.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
Funding
We thank the National Council of Technological and Scientific Development (CNPq; grant 472645/2008) and Coordination for the Improvement of Higher Education Personnel (CAPES; grant 01P04520 - 2013) for their financial support.